The phosphorylation of proteins on tyrosyl residues is now recognized to be an essential element in the control of such fundamental cellular processes as growth and proliferation, differentiation, cytoskeletaI function and the cell cycle. We are currently witnessing an outstanding period of progress in characterizing the structure, regulation and function of both protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), the coordinated action of which governs the levels of cellular phosphotyrosine. The objective of this Third Meeting on "Tyrosine Phosphorylation and Cellular Signaling" is to provide a format in which the study of PTKs and PTPs will be integrated to help participants see how their results contribute to the overall "big picture." We will organize the sessions based around physiological processes and cellular functions, rather than around particular categories of enzymes, so as to try and provide a biological context. With the exception of the Keynote Addresses by Ray Erikson and Sara Courtneidge, all speakers will be selected from submitted abstracts. This will allow emphasis to be placed on encouraging graduate students, postdocs and young independent investigators to present the talks. It also should facilitate the presentation of the most recent and "hottest" results. We anticipate an attendance of 300-350 of which 64 will give oral presentations and approximately 160 will present posters. The funds requested in this proposal will enable more young investigators to participate, especially those who do not yet have independent funding. We hope that the integration of research on PTKs and PTPs at this meeting, placing emphasis on the biological roles of these enzymes, will engender a sense of cohesiveness and communication across the field.